A portable electrochemical microsensor for in-site measurement of dissolved oxygen and hydrogen sulfide in natural water

Dissolved oxygen (O2) and hydrogen sulfide (H2S) are two important indicators of water quality, their levels are of intimate dependence and varying over time. It is of great significance to monitoring of dissolved O2 and H2S simultaneously in natural water, yet has not been reported because of lack of effective approaches. In this work, a portable electrochemical microsensor was developed for simultaneously quantifying dissolved O2 and H2S. Here, Pd@Ni nanoparticles (NPs) were self-assembled onto the microelectrode by MXene titanium carbide (Ti3C2Tx), which were of responsibility towards O2 and H2S detection within single electrochemical reduction process. On this regard, Pd NPs facilitated catalyzing the electrochemical reduction of O2, while Ni NPs were employed as recognition element for H2S detection. With the electrochemical reduction sweep, the initial application of a positive voltage rendered the Ni to be oxidized to be Ni ions, contributing to their following capture of surrounding S2- to form nickel sulfide. Nickel sulfide with highly electrochemical activity were capable of generating detecting reduction current. In consequence, the as-designed microsensor can simultaneously determine O2 concentrations ranging from 36 to 318 μM and H2S levels ranging from 0.1 to 2.5 μM with high selectivity. Finally, the portable microsensor was successfully applied to simultaneous detection dissolved O2 and H2S in natural water in-site, the results of which were comparable to the classical methods.